Unveiling the Metabolic Milieu of Tertiary Lymphoid Expansion

The progression of CKD is strongly shaped by the abnormal accumulation and activation of immune cells within the kidney. While inflammatory cell infiltration is a common feature across chronic kidney disorders, it has become clear that a subset of these infiltrates—tertiary lymphoid structures (TLSs)—play a particularly influential role.¹ TLSs are inducible lymphoid aggregates that arise under persistent inflammatory conditions in diverse settings, including autoimmunity, infection, and aging.² Similar to secondary lymphoid organs, TLSs possess the cellular and structural machinery required to initiate and perpetuate adaptive immune responses. Within the kidney, they are composed of lymphocytes, dendritic cells, fibroblasts, and stromal cells that together create a microenvironment capable of sustaining local immune activation.

TLSs are now recognized across a broad spectrum of kidney diseases, including lupus nephritis, ANCA-associated vasculitis, IgA nephropathy, chronic allograft rejection, and recurrent infections such as pyelonephritis.³ Their presence is associated with persistent inflammation, maladaptive repair, and adverse clinical outcomes. Yet despite their clinical significance, one fundamental question has remained largely unanswered: What fuels TLS? Immune structures of this magnitude and complexity require substantial metabolic support, but the nature and source of those metabolic resources within the kidney microenvironment have until now remained obscure.

In this issue of JASN, Arai et al. provide important new insights into this question.⁴ Using a comprehensive multiomics approach, they characterize the metabolic architecture of renal TLS and identify GSH metabolism as a central feature of TLS biology. Their findings reveal that dendritic cells and fibroblasts within TLS synthesize and supply GSH to lymphocytes, forming a previously unrecognized metabolic symbiosis that supports TLS maintenance. The authors begin by defining the biochemical environment in which TLS develop. Through imaging mass spectrometry and metabolomic profiling, the authors confirm that the kidney cortex is strikingly enriched in cysteine and cystine compared with organs such as liver or brain.^5,6 This provides a metabolically privileged landscape in which cysteine-dependent processes can occur at scale. Against this backdrop, TLSs emerge as foci of intense metabolic activity. The study reveals substantial accumulation of glutathione—a tripeptide antioxidant essential for counteracting oxidative stress—within TLS, coupled with local cysteine depletion. This spatial pattern is characteristic of sites with active GSH synthesis. Consistent with this notion, TLSs across diverse models—ischemia-reperfusion injury (IRI), unilateral ureteral obstruction (UUO), and IgA nephropathy—display elevated oxidative stress markers such as 4-hydroxynonenal and 8-hydroxy-2′-deoxyguanosine.⁷ Such oxidative stress, the authors argue, is not merely incidental but a key driver of metabolic reprogramming within TLS. These findings point to an important shift in how TLS should be viewed: Rather than passive immune aggregates, they represent metabolically active structures responding to and shaped by the oxidative environment of chronic kidney injury. Importantly, this metabolic signature was consistent across multiple disease contexts—including IRI, UUO, and IgA nephropathy—suggesting that altered GSH metabolism is a unifying characteristic of renal TLS.

A major conceptual advance in this study is the identification of the cellular source of GSH within TLS. Lymphocytes, which constitute a major component of TLS, do not express Slc7a11, the cystine/glutamate transporter required for cystine uptake and subsequent GSH synthesis. This raises an important question: How do lymphocytes meet their redox and metabolic needs within the oxidative TLS microenvironment? Arai et al. show that dendritic cells and fibroblasts within TLS express Slc7a11 and are therefore capable of cystine uptake and GSH production. These stromal and antigen-presenting cells supply GSH to neighboring lymphocytes, enabling them to maintain redox balance and function effectively. While previous studies have shown that dendritic cells and fibroblasts can provide cysteine/GSH to maintain lymphocytes,⁸ this study goes beyond this general principle, revealing how they precisely organize metabolic collaboration in the pathological structure of TLS and how this collaboration is functionally indispensable. This metabolic interdependence represents a form of stromal–immune cooperation that extends beyond the established roles of antigen presentation and cytokine signaling. While only a fraction of dendritic cells and fibroblasts express Slc7a11, this limited population appears sufficient to maintain high GSH levels across the TLS. This observation suggests the presence of efficient mechanisms for metabolite distribution or amplification that merit further investigation.

To test whether this symbiosis is essential for TLS maintenance, the authors used both in vivo and in vitro approaches targeting System xc-, the cystine/glutamate antiporter central to GSH production. Pharmacologic inhibition with sulfasalazine—an established but nephrotoxic System xc- inhibitor—dramatically suppressed TLS formation in aged IRI and UUO models. Renal GSH and Cys-Gly levels decreased, confirming metabolic disruption at the tissue level. Complementary in vitro experiments demonstrated that genetic knockdown of Slc7a11 in dendritic cells or fibroblasts, or pretreatment with sulfasalazine, markedly reduced intracellular GSH levels in cocultured T cells. Collectively, these findings show that stromal cell–derived GSH is essential for TLS maintenance and that System xc- represents a central metabolic node regulating TLS formation. However, the nephrotoxicity of sulfasalazine limits its immediate translational potential.⁹ Future work must focus on safer and more selective System xc- inhibitors or alternative strategies to modulate stromal–immune metabolic exchange. Although targeting System xc- effectively disrupts the metabolic support required for TLS, it also intersects with pathways essential for renal cell protection. GSH is a key intracellular antioxidant that detoxifies reactive oxygen species and limits inflammation-induced injury in kidney tissues.¹⁰ Thus, strategies that deplete GSH to impair TLS formation introduce an important dilemma: Inhibiting a pathway crucial for TLS survival may simultaneously impair renal antioxidant defenses. This highlights the need for therapeutic approaches that selectively target pathological TLS metabolism while preserving essential cytoprotective redox functions.

To probe for a noninvasive diagnostic strategy, the authors identified elevated urinary GSH as a highly accurate biomarker for detecting TLS in the kidney. The authors demonstrated that this local metabolic activity of GSH synthesis in TLS is reflected systemically through elevated urinary GSH levels in both murine models and humans with IgA nephropathy. Of particular clinical significance is the identification of urinary GSH as a noninvasive biomarker for detecting TLS in patients with IgA nephropathy. This finding is significant, as a multivariable model combining urinary GSH and eGFR achieved an impressive area under the curve of 0.92 for predicting TLS presence, highlighting its high diagnostic accuracy. By providing a practical, noninvasive approach to identify renal TLS, a pathological feature strongly linked to disease progression that traditionally requires invasive biopsy for assessment. Future studies should assess urinary GSH across other TLS-associated conditions, including lupus nephritis and transplant rejection, to determine its generalizability and potential role in clinical algorithms.

Overall, the work by Arai et al. provide a cohesive framework for understanding TLS as metabolically specialized niches within the kidney. By demonstrating that stromal cells support lymphocytes through System xc–dependent GSH synthesis and transfer, the authors identify a fundamental mechanism underpinning TLS persistence. This metabolic interdependence adds a new dimension to the study of intrarenal immunity and highlights potential therapeutic targets for modulating TLS-driven disease progression. At the clinical level, urinary GSH represents a practical, noninvasive biomarker with the potential to improve disease monitoring and risk stratification in CKD. Leveraging metabolic markers to detect TLS could enable earlier intervention or more precise assessment of disease activity. Overall, this study integrates metabolic profiling, spatial tissue analysis, and functional perturbation to provide comprehensive insight into the metabolic regulation of TLS. It establishes GSH metabolism as a central organizing principle of TLS biology and sets the stage for future work exploring metabolic pathways as therapeutic and diagnostic avenues in kidney disease.

Disclosures

Disclosure forms, as provided by each author, are available with the online version of the article at http://links.lww.com/JSN/F553.

Author Contributions

Conceptualization: Qi Cao.

Writing – original draft: Qi Cao.

Writing – review & editing: Qi Cao.

Funding

Q. Cao: National Health & Medical Research Council of Australia (2008347 and 2012351) and National Natural Science Foundation of China (82370748).